Lago is an open-source Stripe Billing alternative.
This library will allow you to build an entire billing logic from scratch, even the most complex one. Lago is a real-time event-based library made for usage-based billing, subscription-based billing, and all the nuances of pricing in between.
The official Lago documentation is available here : https://docs.getlago.com
The contribution documentation is available here
Check the wiki guide
Lago is open-source under the GNU Affero General Public License Version 3 (AGPLv3) or any later version.